13 replies to this topic

[minituga]

Hi guys
My Mini has a Austin 1300 engine and it was fully rebuilt.
Today I measured the compression of the cylinders and it says 10kg.
is this good or bad?

thank you.

[Ouster]

If you mean 10 kg/cm^2, then that's 140 psi. Do all the cylinders have the same reading?
140 psi Seems a little low for a rebuilt engine.

[Ethel]

The main thing is that they are all about the same, a stronger battery & starter (engine turns faster) will give a higher reading so it's hard to make comparisons.

[bmcecosse]

!0 bar = 147 psi, and yes as above - it's not great - in fact, quite poor! Try again - you need hot engine (10 mile run ) with fully charged battery - all plugs out - and throttle held open. Crank it till it settles on each cylinder in turn. Then - squirt a bit of engine oil into each bore and repeat - if the pressures jump up quite a bit this tells you the rings/bores/pistons are knackered. Report back your findings! With them all being the same - it doesn't look like there are any valve issues.

[Sprocket]

Nothing wrong with 10 bar. All depends on the static compression ratio cam duration and timing If the readings are all the same or at least within 10% of each other, there is not much wrong with the engine condition.

Edited by Sprocket, 27 October 2009 - 11:21 PM.

[bmcecosse]

A good engine will be 170 psi - a very good engine will be 200 psi +. 147 is very mediocre - ok it will run, but not giving great power or fuel efficiency.

[Sprocket]

A good engine will be 170 psi - a very good engine will be 200 psi +. 147 is very mediocre - ok it will run, but not giving great power or fuel efficiency.

Speak for your self, my 16 valver gives an even 10 bar compression (Which is infact the figure quoted for the Motorbike), with a static compression ratio of 11.5:1produces 107bhp and 32mpg with a 3.7 final drive. Are you going to tell me this engine is worn out?

We do not know enough about the engine to determine whether 10 bar is good or not

I stand by my first statement

Edited by Sprocket, 28 October 2009 - 12:03 AM.

[SolarB]

Don't worry Minituga, Sprocket is quite right. Figures from a dynamic compression test are affected by many things, none of which we know.

[minituga]

When i tested it, the engine was cold.

thank you guys.

[minituga]

this is the reading from a friend of mines Mini.
it was rebuilt 1 month ago.

[bmcecosse]

Well - i've compression tested many different A series engines - and even with 300 degree cam etc - have regularly seen 200 psi on good condition engines. I can't comment on 16 v engine - not done that! My own 1340 engine with 544 cam and not particularly high compression ratio used to show 180 psi, and my 1098 with 940 head etc shows 170 psi. So I also stand by my comment that 147 psi is poor! But - we await the hot test - it will be much better, I'm sure.

Edited by bmcecosse, 29 October 2009 - 09:21 PM.

[minituga]

this particullar engine has a kent 286, and was done in cold also.
tomorrow will let mine run until temperature is N and test it.

[Sprocket]

this particullar engine has a kent 286, and was done in cold also.
tomorrow will let mine run until temperature is N and test it.

Not knowing the static compression ratio, but with the information above, 10 bar is about right for a 286 duration cam set at around 106 or 107 degrees at full lift, and a cold engine

Edited by Sprocket, 29 October 2009 - 11:40 PM.

[Sprocket]

My own 1340 engine with 544 cam and not particularly high compression ratio used to show 180 psi, and my 1098 with 940 head etc shows 170 psi. So I also stand by my comment that 147 psi is poor! But - we await the hot test - it will be much better, I'm sure.

1340? short stroke 73.5mm bore?

what do you mean by 'not particularly high compression ratio'? You dont know? I recon it was 11.5:1 at the very least, by my calculations with a compression figure of 180psi, either that or the cam timing is way too retarded, not a particularly low compression ratio by my reckoning

What you have to consider that the math is rarely matched to the actual engine, in the respect that even if you did acurately measure everything, the calculated compression figure will never match the actual test pressure. the actual pressure is always lower.